Heat Exchanger for Drain Heat Recovery

ABSTRACT

A heat exchanger includes an upright center tube for connection to a drain line and an outer tube surrounding the upright center tube so as to define an annular space for connection to a supply line. Baffle portions are received within the annular space between the upright center tube and the outer tube and so as to be arranged to induce turbulence in the annular space while permitting the flow to remain in a substantially axial direction of the tubes. Sleeves may be used to connect the ends of the outer tube to the center tube so as to define a single wall portion of the center tube between the sleeves and double wall portions of the center tube where the center tube is overlapped by the sleeves such that the double wall portions are open axially outwardly and externally at the end of the outer tube.

This application claims the benefit under 35 U.S.C. 119(e) of U.S. provisional application Ser. No. 61/496,633, filed Jun. 14, 2011 and U.S. provisional application Ser. No. 61/577,164, filed Dec. 19, 2011.

FIELD OF THE INVENTION

The present invention relates to a heat exchanger for exchanging heat between a first fluid flow in a drain line and a second fluid flow in a water supply line, and more particularly the present invention relates to an upright center tube and a surrounding outer tube arranged for connection with the drain line and the water supply line to receive the first and second fluid flows respectively.

BACKGROUND

Various devices for recovering heat in waste water are known to reduce energy consumption in heating supplied water. Examples of typical heat exchanger devices are disclosed in U.S. Pat. Nos. 4,352,391 by Jonsson and 4,619,311 by Vasile et al. In each instance, a central drain tube receives waste water from a plumbing fixture in a building. A jacket surrounds the center drain tube to define a space therebetween which receives the flow of supply water in a counter flow configuration such that heat from the waste water in the drain is transferred to the supplied water in the jacket while the flows remain separated from one another. The open annular configuration of the jacket space receiving the supply water in each instance typically causes the supply water to flow in a laminar configuration in a direct path between inlet and outlet ports of the jacket such that heat is only exchanged with a thin film of the water in direct contact with the center tube which reduces the efficiency of the heat transfer due to the boundary layer formed about the center tube.

A common variation to a heat exchanger for recovering waste water heat is disclosed in U.S. Pat. No. 7,322,404 by Van Decker et al. and US Patent Application Publication 2009/0139688 by McLeod. In each instance the supply water tube is arranged as a helical tube about the outer circumference of the central drain tube. While this overcomes the problem of short circuiting in the examples noted above, the flow through the helical supply tube remains substantially laminar such that the boundary layer in the fluid flow forming a thin tube along the surfaces in contact with the drain tube is the only volume of water effectively exchanging heat such that the efficiency remains limited.

SUMMARY OF THE INVENTION

According to one aspect of the invention there is provided a heat exchanger for use between a drain line having a first fluid flow therethrough and a supply line having a second fluid flow therethrough, the heat exchanger comprising:

an upright center tube extending longitudinally between opposing top and bottom ends;

the upright center tube being arranged for connection to the drain line so as to receive the first fluid flow longitudinally through the upright center tube;

an outer tube surrounding the upright center tube so as to define an annular space between upright center tube and the outer tube which spans longitudinally along the upright center tube between opposing top and bottom ends of the outer tube;

the outer tube being arranged for connection to the supply line so as to be arranged to receive the second fluid flow longitudinally through the annular space between the upright center tube and the outer tube; and

a plurality of baffle portions received within the annular space between the upright center tube and the outer tube and so as to be arranged to induce turbulence in the second fluid flow while permitting the second fluid flow to remain in a substantially axial direction of the tubes.

By providing baffle portions which span only partway across the annular space between the upright center tube and the outer tube, the flow in the annular space remains generally in the longitudinal or axial direction, but the baffle portions induce turbulence in the flow so as to disrupt the boundary layer and encourage mixing of the flow so that a greater volume of the flow comes into direct contact with the center drain tube for optimal heat transfer efficiency.

According to a preferred embodiment the baffle portions may comprise wire members received in the annular space which have a diameter which is equal to or less than half a radial dimension of the annular space.

Preferably the wire members include a first wire member wound helically about the center tube in a first direction and a second wire member wound helically about the center tube in a second direction opposite to the first direction such that the first and second wire members overlap and intersect one another in a crosswise manner at a plurality of locations axially spaced along the center tube.

In preferred embodiments at least one outer end of the outer tube is joined to the center tube by an auxiliary sleeve supported about the center tube so as to define a double wall portion of the center tube at the auxiliary sleeve and a single wall portion of the center tube at an intermediate location between opposing ends of the outer tube which is not overlapped by the auxiliary sleeve.

Preferably the auxiliary sleeve is joined to the outer tube at a location which is spaced axially outward in relation to a connection between the between the auxiliary sleeve and the center tube, and an annular space between the center tube and the auxiliary sleeve at the double wall portion is open axially outwardly and externally of the center tube at the outer end of the outer tube.

Preferably both ends of the outer tube are joined to the center tube by an auxiliary sleeve such that the single wall portion is defined between the auxiliary sleeves.

Preferably the single wall portion is longer in an axial direction than the double wall portion.

Preferably the auxiliary sleeve portions are thinner in radial thickness than the single wall portion of the center tube such that the center tube will fail from erosion at the double wall portion prior to failing at the single wall portion.

The center tube may be thinner in radial thickness at the double wall portion than at the single wall portion thereof.

The outer tube may also thinner in radial thickness than the single wall portion of the center tube and the auxiliary sleeve members such that the outer tube will fail from erosion before the center tube.

The auxiliary sleeve preferably protrudes axially outward beyond the respective outer end of the outer tube and the center tube preferably protrudes axially outward beyond an outer end of the auxiliary sleeve. In this instance, the connection of the outer tube to the sleeve and the connection of the sleeve to the center tube does not interfere with an annular space between the center tube and the auxiliary sleeve at the double wall portion being open axially outwardly and externally of the center tube.

The end of the center tube may be enlarged in inner diameter at an end portion overlapped by an outer end of the auxiliary sleeve and the outer end of the outer tube such that the end portion is arranged to receive a portion of a drain line therein having an outer diameter which is substantially equal to an outer diameter of the single wall portion.

According to a second aspect of the present invention there is provided a heat exchanger for use between a drain line having a first fluid flow therethrough and a supply line having a second fluid flow therethrough, the heat exchanger comprising:

an upright center tube extending longitudinally between opposing top and bottom ends;

the upright center tube being arranged for connection to the drain line so as to receive the first fluid flow longitudinally through the upright center tube;

an outer tube surrounding the upright center tube so as to define an annular space between upright center tube and the outer tube which spans longitudinally along the upright center tube between opposing top and bottom ends of the outer tube;

the outer tube being arranged for connection to the supply line so as to be arranged to receive the second fluid flow longitudinally through the annular space between the upright center tube and the outer tube; and

at least one auxiliary sleeve supported about the center tube and joining a respective outer end of the outer tube to the center tube so as to define a double wall portion of the center tube at the auxiliary sleeve and a single wall portion of the center tube at an intermediate location between opposing ends of the outer tube which is not overlapped by said at least one auxiliary sleeve;

said at least one auxiliary sleeve being joined to the outer tube at a location which is spaced axially outward in relation to a connection between the between the auxiliary sleeve and the center tube; and

the double wall portion of said at least one auxiliary sleeve being open axially outwardly and externally of the center tube at the respective outer end of the outer tube.

In other embodiments of the present invention as described herein the baffle portions may comprise protrusions formed on at least one of the upright center tube or the outer tube so as to project into the annular space between the upright center tube and the outer tube and so as to be arranged to induce turbulence in the second fluid flow.

The protrusions may be formed on an inner surface of the outer tube to extend generally radially inwardly towards the center tube as well as being formed on an outer surface of the center tube to extend generally radially outwardly towards the outer tube. Preferably each protrusion on the outer surface of the center tube is longitudinally spaced from adjacent ones of the protrusions on the inner surface of the outer tube such that the protrusions alternate between the center tube and the outer tube in a longitudinal direction.

The protrusions may be arranged to span only partway across the annular space between the upright center tube and the outer tube such that second fluid flow remains primarily in the longitudinal direction between longitudinally opposed ends of the outer tube.

The protrusions may comprise annular ribs which are longitudinally spaced apart. The ribs may be of any shape including rounded, squared or angled, and may be of any depth, or any height relative to the based pipe diameter.

A plurality of protrusions may also be formed on an inner surface of the center tube to project generally radially inwardly so as to be arranged to induce turbulence in the first fluid flow.

In some embodiments the protrusions formed on the inner surface of the center tube are aligned with respective recessed areas on an outer surface of the center tube in communication with the annular space between the upright center tube and the outer tube.

In alternative embodiments the protrusions formed on the inner surface of the center tube are aligned with respective ones of the protrusions projecting into the annular space between the upright center tube and the outer tube.

The heat exchanger may further comprise recessed areas formed on an outer surface of the center tube in communication with the annular space between the upright center tube and the outer tube.

In some embodiments the recessed areas may be adjacent to respective ones of the protrusions projecting into said annular space. Alternatively the recessed areas may be longitudinally spaced from respective ones of the protrusions projecting into said annular space.

In further embodiments the protrusions may be arranged in a helical pattern about a longitudinal direction of the center tube.

Preferably the outer tube surrounds the center tube such that there is only a single layer wall between the first fluid flow in the center tube and the second fluid flow in said annular space.

As described herein, in some embodiments the inner tube ribs have some going inward in order to agitate the waste water as it falls along the inside of the tube wall. Other ribs on inner tube may be pointing outward to agitate the fresh water passing over top the external surface of the inner tube.

The protrusions on the outer tube serve to agitate the fresh water passing over the inner surface of the tube. Together with the outward ribs of the inner tube, the ribs work to agitate the fresh water.

Typically the ribs of the inner tube and the ribs of the outer tube alternate along the length of the tubes. This serves to make sure that the entire water stream flowing between to two tubes is agitated well. The alternating nature of the ribs may also be replaced by ribs that are on top of each other so as to pinch the water flow at the same point along the tubes.

The concept of water flowing between tubes, across ribs, whereby the ribs serve to agitate the water, is not limited to ribs. The ribs may be spirals instead, where the spirals on the inner tube and outer tubes do not close in on each other, but rather the water would still spill over the ribs while moving in a somewhat spiral manner instead of a direct axial flow manner.

The heat exchanger in the preferred embodiment is single wall, however the heat exchanger may also be constructed for form a double inner wall between the first and second fluid flows as well. In the instance of a double wall, the center tube may be made of two tubes that are pressed together with or without a space between them.

The fresh water which passes between the inner and outer tubes preferably enters via a pipe at the bottom and leaves via a pipe at the top of the outer tube so as to counter the flow through the center tube.

Various embodiments of the invention will now be described in conjunction with the accompanying drawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partly sectional perspective view of a first embodiment of the heat exchanger.

FIG. 2 is an enlarged portion of the partly sectional perspective view of the heat exchanger in FIG. 1 according to a first variant of the first embodiment.

FIG. 3 is a sectional view of a portion of the wall of the center tube according to a second variant of the first embodiment.

FIG. 4 is a sectional view of a portion of the wall of the center tube according to a third variant of the first embodiment.

FIG. 5 is a perspective view of a second embodiment of the heat exchanger in which the outer tube is shown to be transparent for illustrative purposes only.

FIG. 6 is a sectional view of a connection between the center tube and the outer tube according to a third embodiment of the heat exchanger.

FIG. 7 is a sectional view of the connection between the center tube and the outer tube according to a fourth embodiment of the heat exchanger.

FIG. 8 is a sectional view of the connection between the center tube and the outer tube according to a fifth embodiment of the heat exchanger.

FIG. 9 is a sectional view of the connection between the center tube and the outer tube according to a sixth embodiment of the heat exchanger.

FIG. 10 is a sectional view of the connection between the center tube and the outer tube according to a seventh embodiment of the heat exchanger.

FIG. 11 is a sectional view of the connection between the center tube and the outer tube according to an eighth and preferred embodiment of the heat exchanger.

In the drawings like characters of reference indicate corresponding parts in the different figures.

DETAILED DESCRIPTION

Referring to the accompanying figures, there is illustrated a heat exchanger device generally indicated by reference numeral 10. The device 10 is particularly suited for use in heat recovery from a drain tube of a plumbing fixture in a building for pre-heating the water supply lines to the plumbing fixture from which heat is recovered. For example, the device 10 is connected in series with the drain line of a shower in close proximity to the shower for exchanging heat with the main supply line which supplies water to the faucets of the shower and/or the hot water tank of the same water supply system. Although various embodiments are described and illustrated herein, the common features of the various embodiments will first be described.

The heat exchanger device 10 comprises a center tube 12 comprising a vertical tube arranged to be connected in series with the drain line to receive the first fluid flow of the drain line through the center tube 12. The center tube extends vertically in a longitudinal direction between a top end 14 and a bottom end 16. The top and bottom ends are configured for suitable connection to respective portions of the drain line. The center tube comprises a generally cylindrical tube formed of a material having a high conductivity, such as copper for example. The inner and outer surfaces of the center tube are accordingly similarly generally cylindrical in shape. The diameter of the center tube corresponds approximately to the diameter of the drain tube typically.

The device 10 further comprises an outer tube 18 similarly extending in a longitudinal direction between a top end 20 and a bottom end 22. The outer tube is supported about the center tube to surround the center tube and extend along the center tube in the longitudinal direction along the full length between the top and bottom ends of the outer tube. The outer tube is also generally cylindrical in shape to define respective inner and outer surfaces which are also substantially cylindrical in shape. The outer tube has a larger diameter than the center tube such that the center tube is received concentrically within the outer tube while the single wall of the outer tube remains spaced radially outward from the single wall of the center tube about the full circumference thereof.

The concentric configuration of the center and outer tubes defines a space therebetween extending along the full length of the outer tube between the top and bottom ends thereof which is generally in the shape of an annular cylinder. End walls 24 span the annular gap between the center tube and the outer tube at both top and bottom ends of the outer tube so that the annular space 25 defined between the centre tube and the outer tube comprises an enclosed volume for receiving the second fluid flow of the water supply line therethrough.

An inlet port 26 is connected through the wall of the outer tube adjacent the bottom end thereof which is suitably configured for connection to the water supply line. Similarly an outlet port 28 communicates through the single wall of the outer tube adjacent the top end thereof which is also arranged for connection to the supply line. By connecting the bottom inlet port 26 and the upper outlet port 28 in the appropriate configuration to the water supply line, the flow of fluid from the supply line is directed upwardly through the annular space from the bottom to the top of the outer tube in a counter flow configuration with the first fluid flow of the drain line downwardly through the center tube.

In the various embodiments of the present invention, the annular space includes baffle portions 29 therein which having a thickness in the radial direction of the tubes which is less than the radial dimension of the annular space 25 between the outer diameter of the center tube 12 and the inner diameter of the outer tube 18. The baffle portions 29 are arranged such that the flow through the annular space primarily or substantially remains in the axial direction of the tubes, but the flow is turbulent as it flows over the various baffle portions.

As described herein according to a first embodiment, the invention relates to a tube-in-tube heat exchanger that recovers heat from waste-water as it passes through the inner (drain) tube to the cold, fresh water supply which flows between the inner and outer tubes. In the first embodiment, the inner and outer tubes are each of single wall construction and the tubes have ribbed surfaces which cause the water to agitate or turn over, so that heat is more effectively transferred from the warm waste-water to the copper tube to the cold fresh-water. Copper is approximately 700 times more heat conductive than water. Only the surface film of water transfers its heat quickly. The water must be agitated so that the water touching the surface of the copper changes as it moves along the tube. The agitation of the water by the ribs greatly increases the efficiency of this heat exchanger.

In the first embodiment, the baffle portions 29 are in the form of various protrusions as described in the following. The outer tube locates a plurality of outer protrusions 30 formed thereon such that each of the protrusions protrudes inwardly from an inner surface of the outer tube only partway across the annular space in the radial direction towards the center tube. The radial dimension of the protrusions 30 typically correspond to approximately 25% to 50% of the radial dimension of the annular space.

In the illustrated first embodiment, the outer protrusions 30 are formed by crimping the single wall of the outer tube to define a plurality of generally circular and annular ribs at longitudinally spaced positions along the length of the outer tube between the top and bottom ends thereof.

The inner tube includes a plurality of inner protrusions 32 formed on the outer surface thereof which similarly protrude in a generally radial direction partway across the annular space in an outward direction towards the outer tube. Each inner protrusion is generally centered in a longitudinal direction between an adjacent pair of the outer protrusions on the outer tube. In this manner, the protrusions within the annular space alternate between a protrusion supported on the outer tube and a protrusion supported on the inner tube along the full length of the annular space in the longitudinal direction.

In the illustrated first embodiment, the inner protrusions also comprise generally circular or annular ribs which are spaced apart in a longitudinal direction from one another along the length of the annular space.

The inner tube may also support a plurality of central protrusions 34 on the inner surface thereof at longitudinally spaced positions similar to the spacing of the inner protrusions such that each central protrusion 34 is associated with a respective one of the inner protrusions 32. The central protrusions 34 also comprise generally circular or annular ribs projecting generally in a radial direction inwardly towards a center of the inner tube.

Turning now to a first variant of the first embodiment of FIGS. 1 and 2, the inner protrusions 32 in this instance comprise crimped formations in the single wall of the inner tube such that each inner protrusion forms a corresponding annular grove 36 on the inner surface of the center tube opposite the protrusion on the outer surface. Accordingly, the grooves 36 formed in the inner surface of the center tube are similarly generally circular or annular in shape at longitudinally spaced positions.

The central protrusions 34 in this instance also comprise a corresponding groove 38 when formed of a similar crimping process such that the grooves are located on the outer surface of the center tube opposite the respective protrusions on the inner surface.

As shown in FIGS. 1 and 2 along both the inner and outer surfaces of the center tube, each protrusion on that surface is associated with an adjacent groove with the grooves being ahead of the protrusions in the flow direction. In this manner, as the first or second flows extend generally longitudinally in respective flow directions, the flows each engage a groove followed by a protrusion along the respective surface of the center tube to induce a considerable turbulence into the respective fluid flow. In the annular space the fluid flow is caused further turbulence by the protrusions on the outer tube at spaced positions between the groove and protrusion pairs on the center tube. Along each surface of the center tube in FIGS. 1 and 2, each groove is located directly adjacent a corresponding protrusion.

Turning now to FIG. 3, according to a further variation of the first embodiment, the protrusions on the inner tube may be formed similarly to the previous embodiment to define corresponding grooves on the opposing sides of each protrusion; however, the protrusions on the inner surface in this instance are spaced from the protrusions on the outer surface of the center tube such that along each surface of the tube, each protrusion is spaced apart from its corresponding groove instead of being located directly adjacent one another.

In yet a further variation to the first embodiment as shown in FIG. 4, each inner protrusion on the outer surface of the inner tube may be aligned in the longitudinal direction with a corresponding one of the central protrusions on the inner surface of the inner tube by forming a rib in the single wall where the single wall has an increased overall thickness such that there are no corresponding grooves on either surface of the central inner tube in this instance.

When the heat exchanger device is connected to respective drain and supply lines as described above, the first fluid flow of the drain line directed through the center tube comes into contact with a greater surface area due to the central protrusions 34 along the inner surface while also increasing the turbulence of the flow for optimal mixing and ensuring a greater volume of the fluid flow comes into direct heat exchanging contact with the single wall between the first and second fluid flows. Similarly the alternating protrusions in the annular space receiving the second fluid flow of the supply line also cause considerable turbulence in the second flow to disrupt the boundary layer and ensure mixing and greater contact of a greater volume of fluid with the heat exchanging surface of the single wall center tube between the first and second fluid flows.

Turning now more particularly to the embodiment of FIG. 5, the baffle portions 29 in this instance comprise a plurality of wire members 50. The wires are made of a heat conductive material having a thickness or diameter arranged to only span partway in the radial direction of the annular space 25 between the outer diameter of the center tube and the inner diameter of the outer tube. In this instance, the flow through the annular space remains primarily and substantially in the axial direction while the baffle portions ensure that the flow is turbulent.

Although the baffle portions may comprise any suitable structure for partially obstructing the flow in the axial direction, in the preferred embodiment of FIG. 5 the baffle portions are defined by a first wire member and a second wire member which are helically wound about the center tube in opposing directions from one another such that the wires cross over one another in a crosswise intersecting manner at several axially spaced positions along the length of the annular space. The baffle portions are assembled by initially winding the first wire member helically upward in a first circumferential direction substantially along the full length of the annular space between the top and bottom ends. Subsequently, the second wire member is wound about the first wire member to extend helically upward in the opposing circumferential direction. When the wire members have a diameter corresponding to approximately half of the radial dimension of the annular space as in the illustrated embodiment, at each intersecting cross over of a second wire member extending overtop of a first wire member, the combined thickness in the radial direction may substantially fill the radial dimension of the annular space at the cross over point to further obstruct the flow and encourage turbulent flow in the axial direction.

In other embodiments, various heat conductive materials can be used which have a thickness which is less than the radial dimension of the annular space such as mesh materials (or strand materials like steel wool) comprised of many individual wire members in crosswise intersecting configurations relative to one another to ensure a turbulent flow around the wire members in the axial direction.

In yet further embodiments, the baffle portions 29 may be formed by various forms of textured surfaces on the outer surface of the center tube or the inner surface of the outer tube such as protrusions defining the baffle portions or recesses defining baffle portions therebetween which encourage turbulent flow.

As described above with regard to FIG. 5, the gap between the inner and outer tubes has spiral wrapped wires. One wire or set of wires fills approximately half the gap thickness and is wound in one direction. The other wire or set of wires is wrapped on top of the first wire and fills approximately the other half of the gap space. This wires force the water to agitate, turn over as it flows along the length of the tube space. The gap space may be filled with any other obstacles which cause the laminar flow to be disrupted, and the water is constantly ‘turned over’ so that heat transfer from the inner tube surface contacts a new surface film of cooler water. Like making scrambled eggs, turning over the surface film of water touching the inner tube continuously puts previously non-contacted water against the inner wall. This process rapidly transfers more heat into the water in the gap space. Gap space may have spirals of wire or any other material that is wire-like in shape. Gap may have non-spiral wound wire. Gap may have any obstruction method which serves to disrupt laminar flow and agitate the water flow so as to break the surface film with a new film to transfer more heat to the water occupying the entire gap space.

Turning now to FIGS. 6 through 11, various embodiments of the connection of the ends of the outer tube to the center tube will now be described. The embodiments of FIGS. 6 through 11 include the baffle portions of FIG. 5.

In each instance of FIGS. 6 through 11, a double wall portion is defined on the center tube which can be used with any of the embodiments of the baffle portions described above. As in previous embodiments, a main portion of both the center tube and the outer tube remains single wall in construction, however in the new embodiments, a pair of auxiliary sleeves 60 are supported at respective axially opposed ends of the outer tube for defining a respective pair of double wall portions 67 on the center tube. In further arrangements, a double wall portion 67 may be defined at only one end of the main single wall portion by only using one auxiliary sleeve 60 mounted at that end.

In each instance, when used at one or both ends of the central single wall portion, the auxiliary sleeve 60 is mounted in close fit arrangement with the center tube such that the inner diameter of the auxiliary sleeve substantially corresponds with the outer diameter of the portion of the center tube upon which it is received. When two sleeves 60 are used, the sleeve portions are axially spaced apart along the center tube with the inner ends 62 being closest to one another and the outer ends 64 being opposite one another at the opposing top and bottom ends of the outer tube 18 respectively.

The inner ends 62 in each instance are joined to the center tube by brazing or other suitable joining means such that each auxiliary sleeve defines the respective double wall portion 67 of the center tube at the respective sleeve and a single wall portion 66 is defined on the center tube between the auxiliary sleeves. More particularly, the single wall portion 66 is the portion of the center tube 12 surrounded by the outer tube 18, but not overlapped or surrounded by one of the auxiliary sleeves 60.

The outer tube is joined at the opposing top and bottom ends thereof to respective ones or the outer ends 64 of the two auxiliary sleeves 60 in the preferred embodiments. Alternatively, when an auxiliary sleeve 60 is only provided at one end, the opposing end of the outer tube is joined to the center tube.

In either instance the annular space remains defined between the single wall portion of the center tube and the outer tube along the central portion, as well as between the outer diameter of the auxiliary sleeves and the inner diameter of the outer tube at the double wall portions where auxiliary sleeves 60 are provided. The opposing top and bottom ends of the outer tube may be joined to the respective sleeves or the center tube either by tapering inwardly or by use of end walls 24 as described above with regard to the previous embodiment.

The inlet and outlet ports 26 and 28 remain located adjacent the opposing top and bottom ends of the outer tube as described above such that each port is aligned with a respective one of the double wall portions in the axial direction.

Each auxiliary sleeve defines a portion of the inner boundary wall of the annular space towards the respective end of the annular space while the single wall portion 66 of the center tube defines the inner boundary of the annular space along a central portion thereof. The outer tube defines the outer boundary of the annular space along the full length of the annular space in the axial direction.

The auxiliary sleeve 60 is formed of material having a radial wall thickness which is thinner than the single wall portion of the center tube such that any erosion at the inner boundary at the annular space is likely to occur in the auxiliary sleeve forming the double wall portion before any failure of the single wall portion. A failure at the auxiliary sleeve would result in leakage within the double wall structure between the center tube and the annular sleeve 60 surrounding the center tube at a location outward from the brazing connection between the two components such that the leakage is directed axially outward towards the top or bottom end of the outer tube where it can be discovered prior to any contamination between the flow through the center tube and the flow through the annular space.

The auxiliary sleeves are much shorter than the central portion of the center tube therebetween in the axial direction such that the area of the single wall portion of the center tube is much larger than the area of the double wall portion defined by the auxiliary sleeves.

The outer tube which defines the outer boundary of the annular space along the full length thereof is typically formed of material that has a thickness in the radial direction which is thicker than the center tube and more particularly the single wall portion of the center tube because larger diameter tubes require thicker walls in order to maintain the same psi rating.

In alternative embodiments however the outer tube may optionally be thinner than the center tube. In this instance, any failure due to erosion of the boundary surfaces of the annular space is more likely to occur at the outer tube where it is visible and does not cause contamination between the first and second flows.

In each instance in the embodiments of FIGS. 6 through 11, both outer ends of the outer tube are joined to the center tube by an auxiliary sleeve 60 supported about the center tube so as to define the double wall portion of the center tube at the auxiliary sleeve and the single wall portion of the center tube at an intermediate location between opposing ends of the outer tube which is not overlapped by the auxiliary sleeve. The single wall portion is longer in an axial direction than the double wall portion.

Furthermore in the embodiments of FIGS. 6 through 11, the auxiliary sleeve is joined to the outer tube at a location which is spaced axially outward in relation to a connection between the between the auxiliary sleeve and the center tube. More particularly, the auxiliary sleeve is typically connected to the center tube at the inner end of the sleeve and to the outer tube at the outer end of the sleeve. The annular spaces between the center tube and the auxiliary sleeves at the double wall portions are open axially outwardly and externally of the center tube at the outer ends of the outer tube. When the auxiliary sleeve portion and the double wall portion of the center tube are both thinner in radial thickness than the single wall portion of the center tube any leaks are more likely to occur at the double wall portion and be detected at the open end of the annular space of the double wall portion.

Turning now more particularly to the embodiment of FIG. 6, a center tube has a constant thickness and constant diameter along the length thereof from the single wall portion to the double wall portion in this instance. The continuous nature of the center tube permits the auxiliary sleeve members 60 to be secured thereabout only by a single brazing seam extending about the full circumference of the tube at the inner end thereof with the entire double wall structure between the sleeve and the center tube being arranged to drain axially outward through the respective top or bottom end of the outer tube.

Alternatively, in the embodiment of FIG. 7, the center tube includes a central portion 68 having a first thickness and two end portions 70 abutted at opposing ends of the central portion having a second thickness which is thinner than the central portion. The central portion 68 defines the single wall portion of the center tube while the overlap of the sleeves 60 with the respective end portions 70 substantially define the double wall portions.

In the instance of FIG. 7, the sleeve structures 60 are again joined to the center tube at the inner ends which overlap opposing ends of the central portion 68 such that the inner ends are brazed to a portion of the center tube having the thicker first dimension. The second smaller dimension at the end portions 70 of the center tube thus only communicate with the double wall structure formed by the sleeve 60. In this instance, the thinner section of the center tube is arranged to fail by erosion prior to the thicker central portion which would result in leakage into the double wall section which would in turn be visible as leakage through the outer end of the double wall structure instead of contaminating the flow in the annular space.

The single wall portion or central portion 68 of the center tube may be near the combined thickness of the center tube portion and sleeve 60 portion of the double wall but, is preferably thinner than the combined thickness at the double wall sections as the thinner material has a greater heat transfer efficiency.

The embodiment of FIG. 7 is further distinguished from the embodiment of FIG. 6 by arranging the outer diameter of the center tube to be recessed inwardly at the end portions 70 relative to the central portion 68 by a radial dimension corresponding to the thickness of the sleeves. In this instance, when the outer tube has a continuous internal diameter, the radial dimension of the annular space 25 remains constant across the single wall portion and both double wall portions of the center tube.

In the embodiment of FIG. 7, the central portion 68 and end portions 70 of the center tube and the auxiliary sleeves 60 may be joined to one another by various means. In one instance, the central portion and end portions of the center tube may be joined by a first braze 80 at the internal surfaces thereof with the sleeve structure then being brazed at its inner end to the central portion 68 at a location axially inward relative to the first braze 80.

According to a second configuration, the inner end 62 of the sleeve 60 may be joined by a large continuous solder 82 which joins the inner end 62 to both the end of the central portion 68 and the end of the respective end portion 70 in one step.

In another embodiment, a first braze 80 joins the inner end of the respective end portion 70 to the sleeve at a location spaced outward from the inner end 62 of the sleeve 60. Subsequently, the inner end 62 of each sleeve 60 may be joined to the central portion 68 at a location spaced axially inward from the end portion 70 by a second braze 86. In this instance, both the central portion 68 and the respective end portion 70 are joined to the sleeve by a respective brazing such that the end portions 70 substantially abut the opposing ends of the central portion 68.

Turning now to the embodiment of FIG. 8, the center tube 12, the auxiliary sleeve 60, and the outer tube 18 are arranged substantially as in FIG. 6 described above, with the exception of the outer diameter of the center tube 12 at the double wall portion. In this instance, the outer diameter of the center tube is reduced at the double wall portion so that the thickness of the double wall portion of the center tube is thinner than at the single wall portion. This has the same advantages as described above with regard to FIG. 7 by ensuring that any leaking of the center tube due to erosion from the central flow would be apparent at the double wall section prior to any contaminating leakage through the single wall portion. The auxiliary sleeve 60 is joined to the center tube by a single brazing at the inner end 62 in this instance.

Turning now to the embodiment of FIG. 9, the centre tube 12, the auxiliary sleeve 60, and the outer tube 18 are again arranged substantially as in FIG. 6 described above, with the exception of the outer diameter of the center tube at the double wall portion. In this instance, the outer diameter of the center tube at the double wall portion is provided with scored annular grooves 90 at a plurality of axially spaced apart positions to reduce the wall thickness of the center tube at the grooves 90. This has the same advantages as described above with regard to FIGS. 7 and 8 by ensuring that any leaking of the center tube due to erosion from the central flow would occur at the grooves 90 and be apparent at the double wall section prior to any contaminating leakage through the single wall portion. The auxiliary sleeve 60 is joined to the center tube by a single brazing at the inner end 62 in this instance.

Turning now to the embodiment of FIG. 10, the centre tube is similar to FIG. 7 in this instance in that there is provided a central portion 68 substantially forming the single wall portion and an end portion 70 defining the double wall portion. As in the previous embodiment, the end portion 70 is reduced in wall thickness relative to the central portion so that leakage would more likely occur through the double wall portion than the single wall portion. Furthermore, the outer diameter of the end portion 70 is reduced relative to the central portion 68 such that the end portion 70 can be snugly received within the inner diameter of the central portion. The auxiliary sleeve 60 can thus overlap the end portion 70 of the center tube at the double wall portion with the outer diameter of the auxiliary sleeve being substantially identical to the outer diameter of the single wall central portion 68. This has the advantage of a constant radial gap dimension in the annular spaced when the outer tube has a constant inner diameter. Furthermore, a single braze or solder 92 at the inner end 62 of the sleeve should be sufficient to simultaneously join the outer end portion 70 of the center tube to the end of the central portion 68 of the center tube and join the inner end 62 of the sleeve 60 to the center tube.

Turning now to the embodiment of FIG. 11, heat exchanger is substantially identical to the embodiment of FIG. 8 except for the configuration of the outer ends of the double wall portions of the center tube 12, the outer ends 64 of the sleeves 60 and the outer ends of the outer tube 18. The auxiliary sleeve 60 protrudes axially outward to the outer end 64 beyond the respective outer end of the outer tube. A braze connection 100 is located at the outer end of the outer tube 18 adjacent the outer end of the sleeve, but with a portion of the sleeve protruding beyond the braze connection to join the sleeve to the outer tube 18 about the full circumferences thereof. Similarly, the center tube protrudes axially outward beyond the outer end 64 of the auxiliary sleeve 60 to a respective bottom end 16. The annular space between the double wall portion of the centre tube and the auxiliary sleeve 60 remains open externally at the outer end for leak detection.

Furthermore, as shown in the embodiment of FIG. 11, the center tube includes an end portion 102 associated with the auxiliary sleeve 60 at each end of the outer tube. The end portion 102 is aligned with and overlapped by a corresponding end portion 104 of the auxiliary sleeve such that both the end portions 102 and 104 are aligned with and overlapped by the respective outer end of the outer tube in the axial direction. The end portions 102 and 104 are both enlarged in diameter by expanding the tube after the sleeve 60 is mounted on the center tube. The end portions are expanded such that the outer diameter of the sleeve at the end portion is approximately equal to the inner diameter of the outer tube which is a constant diameter tube between opposing top and bottom ends in this instance. The stepped diameter at the outer end of the sleeve and center tube thus provides the function of an end wall to the annular space receiving the second fluid flow of the supply line therethrough when a connection is made by the braze connection 100. The resulting inner diameter at the end portion of the center tube is also arranged such that the end portion is arranged to receive a portion 106 of a drain line therein having an outer diameter which is substantially equal to an outer diameter of the single wall portion. The inner diameter of the expanded end portion is such as to receive the end piece 106 with its outer diameter equal to the outer diameter of the single wall portion of the inner tube which permits different wall thicknesses of piece 106, given that the outer diameter is the constant dimension for different wall gauges. An additional braze 108 can thus be located about the full circumference of the center tube at the outer end thereof for connection between the center tube and the adjacent portion 106 of drain line without interfering with the open end of the annular leak detection space. As in previous embodiments, a braze connection 110 is also provided at the inner end 62 of the sleeve for connecting the sleeve to the center tube about the full circumferences thereof.

In all instances, the inlet and outlet ports are aligned with the sleeve structure at a location which overlaps the end portion 70 of the center tube by locating the inlet and outlet ports outward in the axial direction of the tubes in relation to any brazing connection of the sleeve 60 to the center tube. As the directional flow change resulting from the inlet and outlet ports increases the likelihood of erosion to take place at a location in alignment with the port, overlapping the port with the end portions 70 ensures that any leakage resulting from erosion at that location aligns with a portion of the double wall structure which is open to the top or bottom ends of the outer tube for leak detection and prevention of contamination between the first and second flows.

As described above with regard to FIGS. 6 through 11, the major portion of the heat exchanger is the single wall, as described earlier, with all its variations of ribs and/or spiral internal water baffles. A smaller portion of the heat exchanger is double wall. The double wall is designed to fail before the single wall portion, so that leak detection is possible. The double wall consists of a double inner wall. The fresh water wall and the drainwater wall. The fresh water wall is thinner gauge than the inner wall of the single wall portion. This is so that in the event of wall thinning over time due to water erosion of the copper pipe, this wall will fail first. This leak causes the fresh water to exit between the double walls and out the end of the heat exchanger, visible and thus prompting the device to be replaced. The drainwater wall is also a thinner gauge than the inner wall of the single wall portion in the embodiment of FIGS. 7 and 11. This is so that in the event of drain wall thinning over time, the drain wall will fail in the double wall portion of the heat exchanger. This will cause the leak in drainwater to be detected and the device will be replaced. The single wall portion need not be the sum thickness of the two double wall portions. Or they may be depending on the local municipality approving the device for use. The thicker the single wall, the less the efficiency, so something less than double is preferred in general. The single inner wall portion may or may not be formed to a narrower diameter at the end where it mates with the double wall portion. A narrower diameter allows the gap between inner and outer walls not to be reduced much or at all, thus not creating a water pressure drop in the double wall portion.

In some instances, more than one heat exchanger device may be provided in parallel with one another with the corresponding pipe joining the center tubes being branched into parallel branches. Similarly any tubing flowing through the annular space is similarly branched into multiple parallel lines in which each parallel line is connected in series from the inlet port to the outlet port of a respective one of the heat exchanger devices.

Paralleling of two or more heat exchanger devices (either single or hybrid or any other style) may be used to increase efficiency. Since heat transfer efficiency is improved with thinner wall thicknesses, there is an advantage to keeping the overall diameter of the heat exchanger pipes small. Larger pipes require thicker walls in order to handle water pressure and to meet minimum acceptable tested PSI values. A single heat exchanger has a flow rate above which the efficiency drops significantly. In order to efficiently capture drainwater heat at higher flow rates than a single heat exchanger can efficiently handle, it may be practical to parallel two or more of these single devices. Again, as opposed to making a single larger diameter heat exchanger with thicker walls which reduce efficiency.

Since various modifications can be made in my invention as herein above described, and many apparently widely different embodiments of same made within the spirit and scope of the claims without department from such spirit and scope, it is intended that all matter contained in the accompanying specification shall be interpreted as illustrative only and not in a limiting sense. 

1. A heat exchanger for use between a drain line having a first fluid flow therethrough and a supply line having a second fluid flow therethrough, the heat exchanger comprising: an upright center tube extending longitudinally between opposing top and bottom ends; the upright center tube being arranged for connection to the drain line so as to receive the first fluid flow longitudinally through the upright center tube; an outer tube surrounding the upright center tube so as to define an annular space between upright center tube and the outer tube which spans longitudinally along the upright center tube between opposing top and bottom ends of the outer tube; the outer tube being arranged for connection to the supply line so as to be arranged to receive the second fluid flow longitudinally through the annular space between the upright center tube and the outer tube; and a plurality of baffle portions received within the annular space between the upright center tube and the outer tube and so as to be arranged to induce turbulence in the second fluid flow while permitting the second fluid flow to remain in a substantially axial direction of the tubes.
 2. The heat exchanger according to claim 1 wherein the baffle portions comprises wire members received in the annular space which have a diameter which is equal to or less than half a radial dimension of the annular space.
 3. The heat exchanger according to claim 2 wherein the wire members are wound helically about the center tube.
 4. The heat exchanger according to claim 2 wherein the wire members include a first wire member wound helically about the center tube in a first direction and a second wire member wound helically about the center tube in a second direction opposite to the first direction such that the first and second wire members overlap and intersect one another in a crosswise manner at a plurality of locations axially spaced along the center tube.
 5. The heat exchanger according to claim 1 wherein the baffle portions comprise protrusions formed on at least one of the upright center tube or the outer tube so as to project into the annular space between the upright center tube and the outer tube and so as to be arranged to induce turbulence in the second fluid flow.
 6. The heat exchanger according to claim 5 wherein the protrusions are arranged to span only partway across the annular space between the upright center tube and the outer tube.
 7. The heat exchanger according to claim 5 wherein the protrusions are formed on an inner surface of the outer tube and extend generally radially inwardly towards the center tube.
 8. The heat exchanger according to claim 5 wherein the protrusions are formed on an outer surface of the center tube and extend generally radially outwardly towards the outer tube.
 9. The heat exchanger according to claim 5 wherein the protrusions comprise annular ribs which are longitudinally spaced apart.
 10. The heat exchanger according to claim 5 wherein the protrusions are formed on both an outer surface of the center tube and an inner surface of the outer tube so as to project into said annular space.
 11. The heat exchanger according to claim 1 wherein at least one outer end of the outer tube is joined to the center tube by an auxiliary sleeve supported about the center tube so as to define a double wall portion of the center tube at the auxiliary sleeve and a single wall portion of the center tube at an intermediate location between opposing ends of the outer tube which is not overlapped by the auxiliary sleeve, the auxiliary sleeve being joined to the outer tube at a location which is spaced axially outward in relation to a connection between the between the auxiliary sleeve and the center tube.
 12. The heat exchanger according to claim 11 wherein both ends of the outer tube are joined to the center tube by an auxiliary sleeve such that the single wall portion is defined between the auxiliary sleeves.
 13. The heat exchanger according to claim 11 wherein an annular space between the center tube and the auxiliary sleeve at the double wall portion is open axially outwardly and externally of the center tube at the outer end of the outer tube.
 14. The heat exchanger according to claim 11 wherein the single wall portion is longer in an axial direction than the double wall portion.
 15. The heat exchanger according to claim 11 wherein the auxiliary sleeve portion is thinner in radial thickness than the single wall portion of the center tube.
 16. The heat exchanger according to claim 11 wherein the center tube is thinner in radial thickness at the double wall portion than at the single wall portion thereof.
 17. The heat exchanger according to claim 11 wherein the auxiliary sleeve protrudes axially outward beyond the respective outer end of the outer tube.
 18. The heat exchanger according to claim 11 wherein the center tube protrudes axially outward beyond an outer end of the auxiliary sleeve.
 19. The heat exchanger according to claim 11 wherein the end of the center tube is enlarged in inner diameter at an end portion overlapped by an outer end of the auxiliary sleeve and the outer end of the outer tube such that the end portion is arranged to receive a portion of a drain line therein having an outer diameter which is substantially equal to an outer diameter of the single wall portion.
 20. A heat exchanger for use between a drain line having a first fluid flow therethrough and a supply line having a second fluid flow therethrough, the heat exchanger comprising: an upright center tube extending longitudinally between opposing top and bottom ends; the upright center tube being arranged for connection to the drain line so as to receive the first fluid flow longitudinally through the upright center tube; an outer tube surrounding the upright center tube so as to define an annular space between upright center tube and the outer tube which spans longitudinally along the upright center tube between opposing top and bottom ends of the outer tube; the outer tube being arranged for connection to the supply line so as to be arranged to receive the second fluid flow longitudinally through the annular space between the upright center tube and the outer tube; and at least one auxiliary sleeve supported about the center tube and joining a respective outer end of the outer tube to the center tube so as to define a double wall portion of the center tube at the auxiliary sleeve and a single wall portion of the center tube at an intermediate location between opposing ends of the outer tube which is not overlapped by said at least one auxiliary sleeve; said at least one auxiliary sleeve being joined to the outer tube at a location which is spaced axially outward in relation to a connection between the between the auxiliary sleeve and the center tube; and the double wall portion of said at least one auxiliary sleeve being open axially outwardly and externally of the center tube at the respective outer end of the outer tube. 